不同pH值下改性瓜胶压裂液的微观伤害机理

Formation Damage Caused by Modified Guar Gum at Different pH

针对常规高pH值改性瓜胶压裂液对储层伤害大的问题,分析了改性瓜胶在不同pH值条件下的交联行为,研制出了一种在低pH值下交联的改性瓜胶压裂液,该压裂液在170s-1下剪切90min黏度达到256mPa·s,破胶液黏度小于5mPa·s,岩心平均综合伤害率约为20%。采用原子力显微镜和扫描电镜研究了滤液和岩心作用的微观结构对体系伤害性的影响。结果表明,常规改性瓜胶碱性交联体系形成的聚合物网较散,经滤失作用后造成液相入侵和网状膜堵塞储层孔隙喉道,严重损害储层渗透率;弱酸性改性瓜胶交联体系在pH值为4.5时交联形成的冻胶具有更强的网状结构,减小了经滤失进入储层的固相颗粒和残胶,对储层裂缝和其他油气渗流通道影响较小。

A modified guar gum developed at low pH is used to formulate a fracturing fluid,which is used in place of guar gum modified at high pH values. The formulated fracturing fluid has a viscosity of 256 mPa·s shearing at 170 s-1 for 90 min,and the fracturing fluid has a viscosity of less than 5 mPa·s after gel breaking. Permeability impairment is about 20%. Laboratory studies show that guar gum fracturing fluid formulated at alkaline solution generates a weak polymer network,leading to invasion of liquid phase into formation through filtration and plugging of pore throat by the network film. Guar gum modified at weak acidic solution(pH 4.5) ,however,give birth to a strong'frozen gel-like' network,which hinders the invasion of solid particles and residue gel into pore throat,much lesser harmful to formation permeability than guar gum modified at high pH.